This invention relates to an electric rotating machine of the type capable of rotating at more than 1,500 rpm.
More specifically, the present invention relates to a lead-out portion of a rotor winding for feeding electric power to an end of the rotor winding of the electric rotating machine from the exterior, and also relates to a method of connection of the lead-out portion.
A conventional feeder lead wire of field coil is of such a construction as disclosed in Japanese Utility Model Unexamined Publication No. 53-96604, and its construction is determined in view of a cooling performance. However, any structural measures have not particularly been taken against the centrifugal force acting on a rising portion of the feeder lead wire.
For example, in the above conventional construction, laminated thin plates are used as the feeder lead wire, and because of their flexibility, the feeder lead wire is flexible with respect to the deformation due to the centrifugal force.
Where the laminated thin plates are not used, a thick plate is bent and is used as the feeder lead wire. In this case, a material of a low hardness having a cold-processing rate of about 25% is used in order to ensure a bending processability.
Even where a copper material of a relatively high hardness is used, the end of the rotor winding is joined to the upper portion of the feeder lead wire by brazing, and therefore the brazed portion has tended to be much lowered in hardness under the influence of the heat generated by the brazing.
Such construction and tendency will now be specifically described with reference to FIGS. 5 to 10.
FIG. 10 is a schematic cross-sectional view of an electric rotating machine. A rotor 30 supported at its opposite ends by bearings 20 comprises a rotatable shaft 40 provided with a rotor core, a rotor winding wound and received in a laminated manner in slots formed in the rotor core, and a support ring 6 shrinkage-fitted on the rotatable shaft 40 to support an end portion of the rotor winding 3 partially projecting axially from the rotor core.
Field current is supplied to the rotor winding 3 from the exterior of the rotor via collector rings 70, a lead wire 5 received in a central bore of the rotatable shaft 40, a terminal bolt 90 and a feeder lead wire 4.
The rotor 30 is rotated by an associated prime mover while generating a magnetomotive force by the field current, thereby generating a rotating field.
The rotating field causes a stator coil 110 to produce electric power, the stator coil 110 being arranged in surrounding relation to the rotor 30.
The stator coil 110 is supported in slots in an iron core 120, and the iron core is supported by a stator frame 130 provided around the iron core.
FIGS. 5 and 6 are an enlarged cross-sectional view and an enlarged perspective view of an end portion (shown in FIG. 10) of the rotor winding partially projecting axially from the rotor core, respectively.
In FIGS. 5 and 6, the rotor 30 has slots 2 (not shown in FIG. 5) formed in a surface thereof and receiving the winding, and the ends of the winding in the direction of the axis of the rotor are connected together to form a magnetic pole.
The thus connected rotor winding 3 is connected at its end to the feeder lead wire 4, and this feeder lead wire 4 extends inwardly of the end of the winding, and is passed into a central hole in the rotor 30. A support ring 6 is shrinkage-fitted on an end portion of the rotor 30 after the winding connecting operation. The end of the winding 3 and the feeder lead wire 4 are connected together in a manner shown in FIG. 7. Namely, the end of the winding 3 is extended substantially in a circumferential direction of the rotor 30, and is connected at its distal end to the end of the feeder lead wire 4 by brazing. Because of the nature of its construction, the feeder lead wire 4 has a rising portion 4a, and the rising portion 4a is connected at its distal end to the end of the winding 3 by brazing. Conventionally, this brazing operation is carried out in a manner shown in FIG. 9. Namely, a Cooling portion 4b spaced a certain distance X from a brazing portion 4c is provided at the feeder lead wire 4, and the brazing operation is carried out while the feeder lead wire 4 is cooled through the cooling portion 4b. The feeder lead wire 4 is made of a copper alloy in order to have a satisfactory electrical performance, and the copper alloy is softened by the head applied for brazing purposes, so that the compression-resistant hardness of the copper alloy tends to be lowered. The above cooling is carried out in order to limit the extent of the metal softening as much as possible.
In the case where a plate of the copper alloy is shaped by forging, it is known that the relation between the stress and the strain as shown in FIG. 8 is provided when heat of around 700.degree. C. is applied to the copper alloy plate. Namely, when the copper alloy plate is thermally affected, a large strain develops in the copper alloy plate even with a small stress.
In the feeder lead wire softened by the heat, a large centrifugal force acts particularly on its rising portion 4a during a high-speed rotation of the rotor, and as a result a compressive strain develops, and during a long period of the operation of the electric rotating machine, such compressive strain is accumulated.
With respect to the above technique, force withstanding the centrifugal force is not taken into consideration when this technique is applied to the rotor of the electric rotating machine subjected to a large centrifugal force, and therefore there has been encountered a problem that the feeder lead wire is abnormally deformed due to a large centrifugal force and also plastically shrink due to a centrifugal compressive force.
When such abnormal deformation or plastic shrinkage develops, the feeder lead wire and its support structural member are displaced out of position from each other, and loads and displacement acting on each of them become excessive, which may cause cracks and a rupture.